Coating of paper webs and the like



Aug. 28, 1962 E. v. AHARA ETAL 3,051,125 COATING OF PAPER WEBS AND THELIKE Filed Aug. 15, 1958 2 Sheets-Sheet l INVENTORS HOWARD S. DEGROOTRALPH A. JOHNSON,JR EDWARD V. AHARA CONSTANTINE .1 smLMuKs BYM ATTORNEYAug. 28, 1962 E. v. AHARA El'AL COATING OF PAPER WEBS AND THE LIKE 2Sheets-Sheet 2 Filed Aug. 13, 1958 INVENTORS HOWARD S. De GROOT RALPH A.JOHNSO N,JR. EDWARD v. AHARA CONSTANTINE ISTALMUKE BY rm, Kw 2... g4,

ATTORNEYS Patented Aug. 28, 1%62 3,951,125 COATING OF PAPER WEBS AND THELIKE Edward V. Ahara, Ralph A. Johnson, Jr., Howard S. De

Great, and Constantine I. Stalmuke, Rumford, Maine,

assignors to Gxford Paper Company, New York, N.Y.,

a corporation of Maine Filed Aug. 13, 1958, Ser. No. 754,753 7 Claims.(Cl. 118-603) The present invention relates to the coating of webs fpaper and like material, and more specifically to improved arrangements,including method and apparatus, for applying coatings to moving webs,whereby high quality coated surfaces of uniform smoothness may beobtained.

Coating of webs, particularly in the paper industry, has een carried outin a variety of ways, one of the oldest of which is known generally asknife coating. Typical arrangements for knife coating employ a suitableknife or blade, which is pressed against a Web, either unsupported orbacked by a roll or belt, for the purpose of spreading a thin,relatively uniform layer of coating material on the web. The coatingmaterial is introduced onto the surface of the moving web, prior to theknife or blade, and, as the web moves past the blade, the coatingmaterial is metered onto the web surface.

A comparatively recent development in the art of knife coating isrepresented by the apparatus illustrated in United States Patent No.2,368,176, to Arthur R. Trist. There, the web to be coated travelsaround or over a backing roll, provided with a resilient surface, and aknife or blade is pressed resiliently against the web supported by theroll. The blade is disposed at an angle of about 60 with respect to theweb surface, with the working edge of the blade pointing in thedirection of web movement, and coating material, applied to the web asit travels toward the blade edge, is metered onto the moving web surfaceby the blade. In some cases, the blade may form, in part, a reservoirfor the coating material. A coating apparatus of the general typeillustrated in the Trist patent is frequently referred to as a trailingblade apparatus, and the terms trailing blade, trailing blade coater, orthe like, as used herein, refer to an apparatus of the general typeshown in the patent, as distinguished from other types of blade or knifecoaters.

Trailing blade coaters of known design are useful and generallysatisfactory for the application to paper webs of coatings of light coatweight (i.e., in the order of 3-5 pounds per side per ream of 3300square feet). However, notwithstanding a substantial commercial need ordesire therefor, conventional trailing blade coaters have not beenadaptable for successful utilization for the application of coatings ofheavy coat weights (i.e., 7 or more pounds per side per ream of 3300square feet). Thus, a conventional coater may be employed with relativesatisfaction for applying a coating or film of light coat weight. But,if the coat weight exceeds, in any appreciable amount, about 7 poundsper side per 3300 square feet, coating defects, such as surfacescratches, streaks, etc., become noticeable and the coated web isusually not commercially acceptable.

Our experimental work has indicated that trailing blade coaters ofconventional design are inherently incapable of applying coatings ofheavy coat weight in a manner such that the coated web is of acommercially acceptable quality. In this respect, the coating materialalways contains or acquires small foreign particles, such as grit, sand,fibers, quartz, etc., and such foreign particles are present even wheresubstantial precautions are taken to filter or otherwise remove them,because foreign matter (e.g., fibers) is continually introduced by themoving web. These foreign particles tend to be trapped at or adjacentthe working edge of the blade and, when this occurs, scratches or othercoating defects will appear. In a coating of light coat weight, theproblem of scratches and other defects is comparatively negligible. Butsuch defects are readily noticeable in a coating of heavy coat weightand usually render the coated web commercially unacceptable.

In accordance with the present invention, novel arrangements areprovided enabling trailing blade coaters to be utilized elfectively forapplying coatings of heavy coat Weight and of a high quality,commercially acceptable nature while at the same time substantiallyimproving the effectiveness of such coaters for the application of highquality coatings of light coat Weight. In this respect, it is recognizedthat, despite preliminary precautions, undesirable foreign particleswill be introduced into the coating material, forming a potential sourceof coating defects, such as surface scratches, streaks, etc.Accordingly, the present invention deals with the handling of thecoating material in such a manner that undesirable foreign particles areeffectively minimized, by a continuous filtration of certain portions ofthe coating material during a coating operation. In addition,recognizing the fact that a period of delay will be incurred between theintroduction of foreign particles into the coating material and thesubsequent filtration of some or all of such particles, the inventionincludes novel arrangements for maintaining foreign particles incirculation in the coating material and thereby minimizing thelikelihood that such particles will cause defects in the web coating.

In one of its more specific aspects, the present invention provides animproved trailing blade coater incorporating a coating materialreservoir of novel design, Which permits a uniform, controlled flow ofthe coating material in the reservoir, Without eddies or undesirablevelocity variations. With the improved reservoir, foreign particles inthe coating material are kept in circulation to the greatest practicableextent until they are removed by filtration. Heretofore, forcingparticles usually deposited in eddy current areas or precipitated towardthe working edge of the blade as portions of the coating material,circulating toward the blade, were caused to undergo a substantialreduction in velocity.

Another specific feature of the invention resides in the provision, in atrailing blade coater having a reservior for holding a supply .ofcoating material, of improved and highly efiicient arrangements forrecirculating portions of the coating material, during coatingoperations, whereby to maintain foreign particles in the coatingmaterial at a practical minimum level. To this end, the invention takesadvantage of circulation phenomena occurring during coating operations,whereby the coating material withdrawn for filtration and recirculationis drawn from areas of high foreign particle concentration. In addition,the coating material withdrawn for filtration and recirculation isadvantageously taken at a volume rate having a predetermined relation tothe volume rate of application of coating material to the web, therelation being such as to assure highly effective filtration and removalof the foreign particles.

Advantageously, the present invention may be incorporated with theinvention described and claimed in the co-pending application of RobertC. Brown et al., Ser. No. 754,752, filed August 13, 1958, for Coating ofWebs and the Like, executed concurrently herewith and owned by theassignee of this application.

For a better understanding of the invention, reference should be made tothe following detailed description, and to the accompanying drawing, inwhich:

FIG. 1 is an enlarged, fragmentary, cross-sectional enemas 3 view of atrailing blade coater incorporating features of the invention;

FIG. 2 is a simplified, schematic representation of the apparatus ofFIG. 1, illustrating arrangements for circulating and filtering coatingmaterial; and

FIG. 3 is a fragmentary elevation view of a trailing blade coaterincorporating the improved features of the invention.

Referring now to the drawing, the reference numeral designates generallya trailing blade coater apparatus, which may, except as hereinafterdescribed, be of generally conventional construction. The coaterincludes a backing roll 11, which is mounted for rotation about an axis(not shown) and is arranged to be driven by suitable means (not shown).The backing roll 11 generally includes a cylindrical shell 12 having anouter cover 13 of rubber or other resilient material.

conventionally, the backing roll 11 has associated therewith suitablemeans (not shown) for delivering thereto a web 14 and removing the webtherefrom. The web 14 travels around and with the roll, as the rollrotates, and, in the illustrated arrangement, the web and backing rollare adapted to move in a clockwise direction.

A supporting frame 50 of the illustrated apparatus includes spaced arms51, on which are slidably supported blocks 52. The blocks 52 havesuitable bearing means for rotatably supporting a shaft 15, the framearms 51 being provided with elongated slots 53 to accommodate the shaft15 in various positions. The shaft 15 has end portions 54 ofnon-circular cross-section, which are received in openings ofcorresponding shape in a reservoir frame 16, the arrangement being suchthat the reservoir frame 16 is effectively fixed to the shaft 15.

One end of the shaft 15 has keyed thereto an arm 55 adapted to beengaged on opposite sides by adjusting screws 56, 57 and, by appropriatemanipulation of the screws, the shaft 15 and reservoir frame 16 may beheld in various rotary positions with respect to the blocks 52. One endof the arm 55 may have a pointer 58 thereon cooperating with a suitablescale 58 to provide an indication of the adjusted position of thereservoir frame.

The blocks 52 are movable on the frame arms 51 by means of fluidactuators 59 mounted on the machine frame '50 and connected to theblocks by links 60 and pivoted levers 61, and inward movement of theblocks is limited by adjustable abutment means 62. The abutment means 62may comprise micrometer-like devices having extendable plungers 63adapted to engage arms 64 carried by the blocks 52. Operation in unisonof actuators 59 on opposite sides of the machine causes the reservoirframe 16 to be moved in a generally radial direction, toward or awayfrom the backing roll 12. And, to assure uniform movement of theopposite ends of the reservoir frame, an equalizer mechanism isprovided, comprising links 65, arms 66, and a shaft 67 keyed to the arms66.

wall 19 which connects the back and bottom walls.

Advantageously, the bottom wall 17 serves as part of a mounting meansfor holding a blade 20, the blade 20 being engaged at one end by ananchor block assembly 21 adapted for slidable movement in a recess 22defined by the bottom wall 17 and by a supporting plate 23. The forwardportion of the blade 20 passes between the forward edges 24, 25 of thebottom wall and supporting plate, respectively, and projects forwardlyand downwardly therefrom a distance determined by the adjustable settingof the anchor block assembly 21. A suitable adjusting screw 26 isprovided in the supporting plate 23 and engages the anchor block 21 toeffect the desired adjustment of the latter. When the coating apparatusis in operation, the projecting portion of the blade 20 forms part ofthe bottom wall of the reservoir and the forward edge of the blade,constituting its working edge, is in pressure contact with the web 14.

Advantageously, the blade 20 is supported loosely between the wall 17and plate 23 to provide for limited floating movement of the blade. Byway of example, a clearance of between 0.004 and 0.012. inch may beprovided. When the blade is deflected, as shown in FIG. 1, the blade issupported along the front edge of the plate 23 and presses upwardagainst the wall 17 a short distance back from the front edge.

In accordance with usual practice, the reservoir includes end walls ordykes 27 of a suitable size and shape to be received closely between thewalls 17-19 of the reservoir and the outer surface of the web passingover the backing roll. The dykes 27 are advantageously provided withmeans, such as peripheral felts 28, which may be adjustable to somedegree, so that the dykes may be fitted in sealing engagement with thereservoir Walls 17-19 and with the web 14. And, in the event the rangeof adjustment of the dykes is insuflicient to accommodate the variousrotary positions of the reservoir, several sets of dykes may be providedin appropriate sizes and shapes to fit properly throughout the desiredrange of reservoir adjustment.

Although the present invention is not necessarily limited by thecharacteristics and disposition of the blade 20, the blade isadvantageously disposed at an angle of between 40 and 50 (measured fromabove the blade) to the web 14. The reasons for this are explained indetail in the beforementioned co-pending application, and it is to beobserved that the present invention is employed to great advantage incombination with the apparatus of that application. However, it iscontemplated that the instant invention may be utilized to advantage inother environments.

Advantageously, the bottom wall 17 of the reservoir has its uppersurface 29 disposed at a small angle with respect to the blade 20, sothat the cross section of the wall tapers toward its forward edge 24.Thus, in the illustrated arrangement, the bottom wall surface 29 isdisposed at an angle of around 7 with respect to the sup ported portionof the blade 20, and the cross section of the wall tapers in a mannersuch that the forward edge of the bottom wall is of minimum thicknessconsistent with providing sufficient supporting strength.

As shown in FIG. 1, the back Wall 18 of the illustrated reservoir isdisposed at a large angle with respect to the bottom wall 17. Theappropriate angle between the walls will vary, depending upon the rangeof blade angle to be used and, in the illustrated apparatus, the angleis approximately 130. The arrangement is such that the back wall extendsin a generally upward, though not necessarily vertical, direction.

In accordance with one of the important aspects of the invention, thespacing between the backing roll and the walls of the reservoir, at anylevel, is less than the spacing at any higher level. Accordingly, wherethe back wall 18 is formed of a substantially flat plate, as in theillustrated apparatus, the lower edge of the back wall lies at an angleA of not less than measured from inside the reservoir, to the radiusline R extending from the rotational axis of the backing roll 11 to thelower edge of the back wall. At the same time, the angle A should notsubstantially exceed 90, for reasons which will become apparent.Accordingly, where the reservoir is capable of rotational adjustmentthrough a range of operative positions, the back wall 18 should lie atan angle of not less than, but not substantially more than, 90 to theradius line R when the reesrvoir is adjusted in a counterclockwisedirection to the limit of its operative range. When the reservoir isadjusted clockwise from the above described limit position, the anglewill, of course, be increased somewhat, by an amount equal to theclockwise adjustment. The operative range of adjustment is usually such,however, that the angle A is not substantially greater than 90 at anytime.

The back and bottom walls of the illustrated reservoir areadvantageously connected by a transition wall 19, which is of arcuateshape, having a relatively large radius of curvature and arranged tomerge with the back and bottom walls in substantially tangent relation,whereby to provide a smooth, unbroken transition between the angularlyrelated surfaces of the back and bottom walls. Alternatively, thereservoir may be formed of a single, continuous, curving wall having, ineffect, bottom and back portions and arranged to provide an unbrokensurface for the smooth flow of coating material. In any case, therelationship of the rservoir wall to the backing roll should be suchthat, at any level, the spacing between the backing roll and the Wall isless than the spacing at any higher level. For the purposes of thepresent description, the term unbroken surface is used to distinguishfrom a configuration of angularly related surfaces meeting at a sharpcorner.

Although it is not intended that the scope of the present invention belimited by the specific dimensions herein stated, in a coating apparatushaving a backing roll of about 40 inches in diameter, the radius ofcurvature of the transition wall 19 may advantageously be in the orderof 4 inches or more, while the back and bottom walls are around inchesand 5 inches respectively.

The improved reservoir configuration described above has severalimportant advantages. Thus, when the coating apparatus is in operation,the web 14 moves at high speed along one side of a body of coatingmaterial contained in the reservoir. The friction between the web andthe coating material tends to cause layers of the material adjacent theweb to move in a downward direction and thereby sets up a circulation ofthe coating material in the manner indicated generally by the arrows inFIG-'1. In prior apparatus the reservoir configuration did not providefor a cross section of the reservoir at any horizontal level to be lessthan the cross section at any higher level and for this reason eddycurrents were set up in the circulating color at points of velocityvariation. This reulted in precipitation or depositing of foreignparticles present in the coating material, with the result-that a largeproportion of the particles found their way tothe Working edge of theblade. The new reservoir configuration, on the other hand, substantiallyeliminates undesirable eddy currents and velocity variations, so thatthe foreign particles are kept in circulation to the greatestpracticable extent. At the same time, the new configuration, in whichthe back wall 18 approximately follows the contours of the backing roll11 'and is spaced therefrom a relatively short distance, provides forarelative volume of the coating material in the reservoir, so thatforeign particles introduced into the reservoir may be disposed of withgreater facility.

In accordance with another important aspect of the invention, improvedarrangements are'provided for recirculating the coating material throughappropriate filter means, during a coating operation, whereby to remove,to the greatest practicable extent, foreign particles introduced intothe coating material during the operation. To this end, the inventiontakes advantage of circulation phenomena which we have observed, thatforeign particles in the coating material tend to migrate in a spiralcourse, during operation of the coater, toward the ends of the reservoirand, in somecases, also toward other localized areas, dependinguponthesize and shape of the reservoir and upon such factors as webspeed, consistency of the coating material, etc. Thus, means areprovided'adjacent the ends of the reservoir and at: other-areas ofparticle concentration for withdrawing portions of the circulatingcoating material and flowing the withdrawn coating material throughappropriate filter means to remove foreign particles therefrom. Theimproved arrangement provides maximum efiiciency in'the removal offoreign particles, since the coating material withdrawn for filtrationand recirculation to the reservoir is taken from areas of naturally highforeign particle concentration.

Referring specifically to FIG. 2 of the drawing, the reservoir of theillustrated apparatus is provided, adjacent each of the dykes '27, withoutlet openings 30, which enter the back of the reservoir slightly abovethe level of the bottom wall 17. Appropriate tubes or conduits 3-1communicate with the openings 30 and join with a conduit 32 leading tothe intake of a pump 33. The pump 33 discharges through a conduit 34into a suitable filter 35, and the filter 35 discharges into a returntube or conduit 36. In the'illustrated apparatus, the return tube 36 isconnected to separate return tubes 37 leading to openings 38 in the backwall of the reservoir, whereby the recirculated, filtered coatingmaterial my be discharged into the reservoir.

In cases where the reservoir is of substantial width, it may beadvantageous to provide one or more additional openings, such as theoutlet opening 39, for withdrawing some of the color from areas spacedfrom the reservoir end walls. The optimum number and location ofrecirculation outlets may vary with reservoirs of different sizes andshapes, but may be determined readily by empirical methods. Thus, areasof particle concentration, in addition to the end areas of thereservoir, may be determined by introducing into a supply of coatingmaterial a quantity of foreign particles, such as sand, fibers, etc.Areas of concentration may be determined by observing the location, onthe coated web, of surface defects. The foreign particles may also bedistinctively colored, if desired, so that their presence in the supplyof coating material or on the coated web is readily ascertainable.Generally, coating'apparatus is adaptable for the accommodation of websof various widths, in which case the reservoir is advantageouslyprovided with a plurality of outlet openings 39 (FIG. 2) which may heused or plugged on a selective basis, so that optimum operatingconditions may be afforded under most circumstances.

In some instances, it may be desirable and advantageous to operate thecoating apparatus with the end dykes 27 r,e moved from the reservoir, inwhich case the coating material is simply allowed to flow out of theends of the reservoir, into suitable collector means (not shown), fromwhich the material is drawn to the pump 33. When the end dykes areremoved, the outflow of material at the ends of the reservoir isutilized to eflfect the eificient removal of foreign particles whichwould otherwise tend to concentrate =at.the ends, although additionalwithdrawal outlets may be utilized at other areas of concentration, ifany, near the center of the reservoir.

The location of the inlet openings 38 is not deemed to be of particularimportance. However, it is usually advantageous to locate the inletopenings near the center portions of the reservoir and adjacent the toplevel of the coating color. l

In order to achieve effective filtration of the foreign particles in thecoating material, recirculation of the material through the filter 35and back to the reservoir should take place at a rate appropriatelyrelated to the rate at which foreign particles are introduced into thereservoir. Accordingly, as one of the specific aspects of the invention,the recirculating system, including the pump,33, is of such capacity asto enable color to be withdrawn for recirculation at a rate notsubstantially less than, and advantageously several times as great as,the volume rate at which the coating material is applied to the movingweb 14. v Withdrawal of coating material at this rate, from areas ofhigh foreign particle concentration, provides for highly efiicientparticle removal from the coating material supply.

As will be readily understood, as coating material is applied to themoving web, during operation of the coating apparatus, additionalmaterial must be supplied to J scopeof the invention,

' the reservoir tomaintain the desired head. of material therein. In,the illustrated system, the make-up material is provided from a supplysource 40 arranged to discharge into the line 32 leading to the intake,of the pump 33.

tageously, the ratezof introducing'make-up material is r 'so adjusted astomaintain the coating material. in the reservoir at a minimum levelconsistent with providing adequate. contact between-the material and themoving web. The optimum level will vary with such factors as machinespeed, viscosity, etc., and may be determinedi by visual, observations.

The new method and apparatus are highly advantageous, in. that thecoating webs may be carried out in environment which is as free aspracticable of foreign particles. Accordingly, extended coatingdefectshere tofore caused by the lodgingrof foreign particles in and around'theworking edge of theblade are substantially minimized, and 'coati'ngsof higher quality and greater coat weight may he applied' While it iscontemplated that the method and apparatus of the present invention maybe incorporated in" coating apparatus of various types, significantadvantages are realized when the teachings of thepresent invention areapplied in combination with the apparatus described and claimed :in' thebeforementio ned' co-pending application: The combined inventions permitthe successful application of highquality web coatings of heavy coatweights substantially free of scratches, streaks, etc., which have beenunobtainable heretofore with trailing blade coating apparatus. Forfurther discussionof the advantages ofthe combined inventions, referenceshould be made to the said co-pending application.

It shouldbe understood that the invention, as specifitherein withoutdeparting from the clear teachings of the disclosure. Accordingly,reference should be made, to the following appended claims indetermining the full 7 What is; claimed is:

lQIn a trailing blade coater for app1ying-a-coating layer directly to amoving web and comprising a websupporting'backing'roll about which a webis passed,,a

reservoir placed against the backing roll for holding a i supply ofcoating materialpand a blade forming in part a wall .of said reservoirand engaging a web moving 7 around said. rolL; the; improvementcharacterized by said reservoir comprising abottom wall disposedat anangle to said backing roll, a back wall-L disposed at an obtuse angle tosaid bottom wall" andextending upward therefrom, and a transition walljoiningsaidback andibottom walls and merging. into substantially tangentrelation H thereto, said" transition Well being of arcuate, form. andhaving a large radius of curvature, said botom, transition and backwalls being so related and soariangedlw ithrer spectto said backing rollthat the; spacing betweenlsa id backing roll and the wallsl of said"reservoir at any level is; less than the spacing at any higher level',andr'duct means 'ent'ering said reservoir at preselected points for rremoval of coating. material"from areas surrounding saidpreselected'points. 1 V V a 1 2.1 1 aftrailing blade coater for applyinga. coating layer directly to a moving web, and comprising a weba' wallof said reservoir and' engaging a web moving reservoir comprising meansincluding saidblade forming a bottom wall, and a back wall extendingdownward toing material from areas surrounding said preselected points.V

3 Thecoater of claim 2, in'which said reservoir isadjustable about anaxis parallel to the backing roll axis, for varying the angle, of saidblade with respect to sa d web, an'd said reservoir has one operativelimit of adjustment in- Which said back wall lies at an angle. of notless than 90 to said radius line and a second operative limit positionin which said back wall lies at an angle of not substantially more than90 to said radius line.

4. In a trailing blade coater for applying a coating layer directly to amoving web and comprising a web-supporting backing roll about which aweb is passed, a reservoir placed against the backing roll for holdingasupply of coating material, and a blade forming in part' a wall of 7said, reservoir and engaging a Web moving around said ca-lly describedherein, 'is intended to be'repre'sentativer i only, as certain changesand variations may be made roll, the improvement: characterized by saidreservoir comprising meansformingt bottom and back walls extendingoutward and upward from said-blade,-said wall forming means forminga'substantially' unbroken surface along which circulating coatingmaterial may flow, and said wall forming means being so arranged anddisposed with respect to said backing roll that the'spacin'g betweensaid ,backing roll and the walls of, said reservoir at any level is lessthan the spacing at anylhigher level, and duct means entering saidreservoir at preselected points for removal of coating material fromareas surrounding said preselected points. 7 a a,

7 5. In a'trailing blade coater for applying acoating, layer directly toamoving web and comprising; a Web-support ing backing roll, about which,a webis passed, a. reservoir o placed againstjthe backing roll forholding a supply of a supporting backing, roll about which a web ispassed, a r reservoir placed against the backingfroll for holding asupply of coating material, and a blade forming in part coatingmaterial, and, ablade formingjin part, a'wall of said-reservoir and;engaging a webhmoving around said roll,v the improvement characterized,by saidreservoir comprising means including; saidblade-forming a bottomwallqdisposed at an 'an'gl'e'to. saidibacking; roll, and means forminga, back wall extending upward from said. bottom wall forming; means,said back, wall following approximately the. contour of saidbacking,roll and being, spaced therefrom at any level a distance. no greaterthan the spacing; atany higher level, and duct meanssentering saidreservoir; at, preselected pointsffor removal of coating material fromareas surrounding: said preselected points. a

V 6. The improvement. of clainr 5., iniwhichsaid'bottom and back wallformi'ngmeans are relatively'iiatrwallpor tions disposed atanobtusefang'le, and altransition wall connects therespectivewall'forming-mean's, said: transition wall -being of arcuate shape. and:having a large radius of curvature; r i i 7; The. improvementof claini5;which includes: filter meanslconnectedin said duct for removal" offoreign particlessfrom coating material flowing therethrough, and

means for circulating said coating material in said 'duct means. v p r Vi References Cited inthe, fileof this patent V UNITED STATES PATENTS1,993,055? Gerstenberg Mar.,5, 1935 $2,328,183 7 Barrett Ailg; 3-1, 19432,399,688" Metzfler et a1. May;7, 1946 [2,649,758? J COWgil1 ,Au'g.,25', 1953

